A resistive random access memory (RRAM) has advantageous properties in numerous aspects, such as simple structure, fast speed, low power consumption, data stability and non-volatility, easy three-dimensional integration and multi-value storage, RRAM has become a hot research topic. The resistance in a resistive random access memory has a varistor behavior and can be changed by applying a voltage or a current to the bottom electrode of the RRAM, showing a low resistance state and a high resistance state for storing a logic “0” and a logic “1”.
A RRAM generally requires a selector to eliminate the sneak leakage path. An NMOS transistor or a PN diode is typically used as the RRAM selector, which is called 1T1R or 1D1R. The 1T1R structure of an RRAM unit includes a transistor and an RRAM cell. The 1D1R structure of an RRAM unit includes a PN diode and an RRAM cell. A RRAM selector requires a high SET current and a high RESET current, small selector size, relatively high breakdown voltage and leakage. However, as the device size shrinks to 40 nm and below, the 1T1R and 1D1R structures cannot meet these design requirements.
At present, the transistor of the 1T1R structure of an RRAM unit can only reach 1/5 to 1/3 of the target specification, the leakage current is 0.5 to t time higher than the target value, and the transistor size is 10 times larger than the required size.
The RAM cell in the 1D1R structure of an RRAM unit should be a unipolar or nonpolar cell. However, the current RRAM unit is bipolar, that means the RRAM unit needs to pass a high forward current to implement the SET process and a high reverse current to implement the RESET process, but the diode can only pass a high current in one direction.
Thus, there is a need for a novel memory unit to solve the above-described problems.